1. Field of the Invention
The present invention relates to a method for cutting a printed circuit board, and more particularly, to a cutting method capable of reducing burrs in metal conducting wires and increasing the quality of printed circuit boards.
2. Description of the Prior Art
The window ball-grid-array (WBGA) package is a novel chip package technology. Connecting wires, which are drawn from a die, of a WBGA packaged memory pass through a window of a load board and connect with contact pads on the load board. Therefore, the connecting wires between the die and the load board are shortest of all of ball-grid-array (BGA) package technologies in existence such that the transmission speed is quicker and the inductance and the noise interference are smaller. For this reason, WBGA packaged memories are more suitable to be applied in a high frequency and high speed operation environment, and because of the short connecting wires WBGA packaged memories have lower power consumption and generate less heat. For instance, memories adopting the WBGA package technology have two to three times more memory capacity than other memories, which have the same size, and have better electric and heat conducting characteristics, so they are widely applied in portable products, for example, desktops and so forth.
A load board of a WBGA packaged memory is fabricated by using printed circuit board compatible processes, and windows of the load board and finished product separations are performed by utilizing cutting mills. FIG. 1 to FIG. 4 are schematic diagrams for illustrating a method for forming a window 26 by cutting a load board 10 of a WBGA packaged memory according to the prior art. As shown in FIG. 1, a substrate 12 is provided after an internal circuit process of the substrate 12 is finished. A plurality of metal conducting wires 14, 16, 18, 20, and 22 consisting of copper are formed on an upper and a lower surface of the substrate 12.
As shown in FIG. 2, a solder-resist ink layer 23 covers a portion of the metal conducting wires 14, 16, 18, 20, and 22. An exposure and development process are performed to increase an adhesive force between the solder-resist ink layer 23 and the metal conducting wires 14, 16, 18, 20, and 22 by light polymerization. As shown in FIG. 3, a conducting layer 24 is plated on the metal conducting wires 14, 16, 18, 20, and 22, which are not covered by the solder-resist ink layer 23. The conducting layer 24 consists of nickel (Ni) or gold (Au). As shown in FIG. 4, a cutting process is performed to form a window 26 by utilizing mill cutting on the substrate 12. The window 26 of a load board 10 of a WBGA packaged memory is finished.
According to the prior art, when a mill is used to cut the load board 10 of the WBGA packaged memory directly to form the window 26, burrs often result in edges where the metal conducting wires 14, 16, and 18 are cut, influencing the quality of the load board 10. In the past, the burrs are removed by laborers, hence manual labor is required and the quantity of output is influenced.